Method And Device For Cleaning Welding Torches With Co2 Dry Ice

ABSTRACT

The invention relates to a process and devices for cleaning welding torches, for example in automated welding lines, on welding robots and in single-piece production, by means of a cold medium, preferably CO 2  dry ice, the CO 2  snow produced by expanding the pressurised liquid CO 2  being directly applied with low density in a uniform or intermittent manner to the surfaces to be cleaned of the contact pipe and gas nozzle by means of a cleaning head that fits the burner.

The invention relates to a method and a device for cleaning weldingtorches in automated welding lines, on welding robots, and insingle-piece production.

Various methods for cleaning welding torches are known. There aremethods that are based on mechanical cleaning. In this connection, oneor more wire brushes, various milling tools, or mold millers are known.

It is a disadvantage in this connection that only the external region ofthe gas nozzle and a part of the contact pipe can be cleaned with thesetools. The deposits of spatters and flue gas in the interior of theburner and the parting agents that are blown in are not completelyremoved. In the case of conical gas nozzles, the interior of the gasnozzle cannot be cleaned using this technology.

Another disadvantage has proven to be the circular configuration of theburner due to the necessary rotational movement of the tools, since thisopposes an adaptation of the burner shape to the seam or point region.Changes in the shape of the burner require a change in the cleaningdevice.

Another disadvantage consists in the fact that the surface of theburner, which is smooth at first and usually nickel-plated, is worn offor roughened up due to the mechanical work. This roughening leads to amore rapid and greater contamination of the burner.

Cleaning using a magnet is also known. For this purpose, the burner isimmersed into a special bath, and the adhering spatters are removedusing a magnet. This cleaning technology is only suitable for ferrousmetals. This method is not suitable for cleaning welding burners usedfor welding Al, stainless steel, or bronze.

A cleaning technology is described in WO 02/49794 that cleans thewelding burner using a CO₂ air mixture, utilizing thermotension, whichoccurs in the case of metals at different temperatures. A disadvantagein the case of this technology is that the contact pipe cannot becleaned completely, since the CO₂ pellets become effective only whenthey directly impact the surface to be cleaned. The rotating jet nozzleincreases the cleaning performance, but cannot become effective all theway to the gas inlet bores. Furthermore, the metering of the pellets inaccordance with the cleaning task and mixing the compressed air streamis a disadvantage. Condensate formation and the related icing up of themetering unit in case of extended down times has also proven to be adisadvantage.

A technology is described in JP 07314142 A that is supposed to preventthe adhesion of spatters. For this purpose, a parting agent is sprayedonto the cold burner before the welding process.

The invention indicated in claim 1 to 3 is based on the problem ofcreating a cleaning method and a device for contact-free cleaning ofwelding burners, independent of whether these are single-wire burners ormulti-wire burners.

This problem is solved, in accordance with claim 1 to 3, by means of amethod for cleaning welding burners, for example in robot cells thatoperate automatically, using a cold jet medium, preferably CO₂ snow,which is blown onto the surface to be cleaned, uniformly or atintervals, and is guided past the surface to be cleaned by means ofcompulsory guidance, whereby the special cleaning head is moved on theaxis of the contact pipe, in linear manner.

According to claim 4 to 7, the device for implementing the methodconsists of a cleaning sleeve that is dependent on the outside diameterof the contact pipe and the inside diameter of the gas nozzle, whichsleeve can be displaced on the common axis of contact pipe and cleaninghead, either in linear manner or at a certain angle to the weldingburner.

The pressure of approximately 50 bar that is required in the uptakebottle or in the tank in order to maintain the liquid phase of the CO₂is used directly for cleaning the outside surface of the contact pipeand the gas nozzle. The liquid CO₂, which is under pressure, is blowninto the cleaning sleeve by way of one or more nozzles at the base ofthe cleaning sleeve, whereby the inflow angle can be different,uniformly or at one or more short intervals. The CO₂ snow that is formedwhen the liquid CO₂ relaxes is immediately used for cleaning, i.e. forsupercooling of the adhering spatters, while at the same time there isslight condensation due to the compulsory guidance in the cleaningsleeve. The condensation is achieved by means of the volume increaseduring relaxation and by means of the limitation of the expansion regionby the inside diameter of the cleaning sleeve. In order for thecondensation of the CO₂ snow not to cause the cleaning sleeve to becomeblocked up, a certain ratio of nozzle cross-section to inside diameterof the cleaning sleeve must be maintained. When using uptake bottlesbelow room temperature, the ratio of 1:13 has proven to be advantageous.The large mass differences between contact pipe and gas nozzle inrelationship to the welding spatters result in more rapid cooling of thespatters and, because of the shrinkage connected with this, loosening ofthe spatters. For pressure equalization in the cleaning sleeve duringrelaxation of the liquid CO₂, the cleaning sleeve can be provided withlateral bores.

Cleaning of the welding burner takes place in at least two stages. Inthe first stage, the adapted cleaning head, with the cleaning sleeve,stands at a distance in front of the gas nozzle that is dependent on theoutside diameter of the gas nozzle. At this distance, cleaning of thegas exit opening of the gas nozzle takes place by means of short-termapplication of CO₂ snow. Subsequently, the welding burner moves into thecleaning sleeve with the contact pipe, and over the cleaning sleeve withthe gas nozzle. With another CO₂ pulse and because of the compulsoryguidance brought about by the cleaning position, the outside region ofthe contact pipe and the inside region of the gas nozzle are cleaned.

The advantage of the invention consists in the fact that because of theuse of the cold jet technique, particularly because of the use of CO₂snow and a cleaning sleeve adapted to the burner, cleaning of theburners can be carried out without contact and without additionalclamping procedures that result in changing the position of the burnerand therefore can be the cause for faulty welds. Limited cooling andloosening of contaminants takes place by means of the CO₂ snow, mainlyas the result of the thermotension that is provoked in this connection,while the CO₂ snow/air stream brought about by the phase transition andpromoted by the compulsory guidance through the cleaning sleeve flushesthe loosened contaminants out.

Another advantage of the invention is that because of the use of CO₂snow, i.e. of the cold jet technique, there is no direct contact withthe welding burner and therefore the surface of the welding burner isnot damaged or worn away.

It is furthermore advantageous that because of the contact-freecleaning, the burner shape can be adapted to the corresponding weldingtask in significantly better manner, and therefore welding in grooves,corners, or in tight regions is simplified or made possible.

A further development of the invention consists in the fact that in thecase of fixed welding burners, the cleaning device is mounted on a sledand the method is implemented, in the individual cleaning positions, bymeans of the sled.

In a continuation of the solution according to the invention, the liquidCO₂ is guided to directly in front of the gas nozzle, within the wall ofthe cleaning sleeve, and immediately blown onto the face surface of thegas nozzle as it relaxes.

In a further continuation of the solution according to the invention,cleaning is carried out with two separate cleaning sleeves. In the caseof multi-wire or tandem burners, the gas nozzle encloses one or morecontact pipes. In the first stage of cleaning, the liquid CO₂ is guidedonto the face surface of the gas nozzle directly, at different inflowangles, from a ring of small nozzles. The ring is adapted to the contourof the gas nozzle. In the second stage, the contact pipe(s) is/arecleaned, whereby the burner is guided by the robot in such a manner thatthe cleaning sleeve is passed uniformly over the contact pipe to becleaned.

An embodiment of the solution according to the invention that goesfurther is cleaning and blowing the burner out from the rear. For thispurpose, the cleaning sleeve is moved directly over the contact pipe,and the liquid CO₂, which is under pressure, is guided forward in thewall of the cleaning sleeve. Because of the relaxation pressure, the CO₂snow is guided both onto the gas nozzle and onto the contact pipe. Boresin the cleaning sleeve make it possible for the CO₂ snow to flow out,and prevent build-up of pressure. This variant of the burner cleaningcan also be carried out in two stages, as already described. In thefirst stage, cleaning of the gas nozzle exit opening takes place, and inthe second stage, cleaning of the inside region of the burner takesplace.

It is obvious that the material, the additive material, and the weldingparameters have an influence on the shape and size of the weldingspatters. This also requires an adaptation of the cleaning device to theexisting working conditions. This adaptation consists of a steppedembodiment of the cleaning sleeve.

As a result of combining the various embodiments according to theinvention, there are additional advantages of contact-free cleaning bymeans of direct adaptation of the cleaning variant to the weldingprocess.

EXEMPLARY EMBODIMENT

In the following, the invention will be explained in greater detailusing four examples. The drawing shows:

FIG. 1: Structure of a cleaning device for single-wire burners

FIG. 2: Structure of a cleaning station for multi-wire burners (tandemburners)

FIG. 3: Replaceable cleaning sleeve with inside bores for targetedguidance of the liquid CO₂

FIG. 4: Stepped cleaning sleeve

EXAMPLE 1

Liquid CO₂ is guided from a CO₂ liquid tank 1 to the valve 3, by way ofa pressure line 2. A measurement device 4 is situated ahead of the valve3, to monitor the liquid CO₂ level. The valve 3 is directly connectedwith the cleaning head 5. The cleaning head 5 is held in the housing 7by means of the nut 6. The cleaning pipe 8 is positioned by means of theunion nut 9. For cleaning, the welding burner 10 is moved from theworking position into the starting position 11, and oriented in such amanner that the contact pipe 12 and the gas nozzle 13 lie on the centerline 14, together with the cleaning pipe 8. After orientation, thewelding burner 10 moves out of the starting position 11 into the firstcleaning position 18. If the measurement device 4 confirms, by means ofthe signal 15, that CO₂ liquid is present, the robot gives the signal 16for opening the valve 3. The liquid CO₂ flows through the nozzleopenings 17 into the cleaning pipe 8 and relaxes, with simultaneousslight condensation, to form CO₂ snow that is blown onto the exitopening of the gas nozzle 13 by means of the pressure in the bottle 1.The required pressure equalization is achieved by means of theequalization bores 20. Once the exit opening of the gas nozzle 13 hasbeen cleaned, the welding burner 10 moves from the first cleaningposition 18 into the second cleaning position 19. In this connection,the contact pipe 12 moves into and the gas nozzle 13 moves over thecleaning pipe 8. Once the position 19 has been reached, the valve 3 isopened by means of the signal 16 and CO₂ snow is again blown into thecleaning pipe 8. Because of the contact pipe 12 being moved in, the CO₂snow is necessarily guided past the contact pipe 12 and the insidesurface of the gas nozzle 13. After successful cleaning, the weldingburner 10 moves back into the starting position 11 and from there intothe working position.

EXAMPLE 2

Liquid CO₂ is guided from a CO₂ liquid tank to the valve 3 by way of apressure line 2. A measurement device 4 is situated ahead of the valve3, to monitor the liquid CO₂ level. The valve 3 is directly connectedwith the cleaning head 5. The cleaning head 5 is held in the housing bymeans of the nut 6. The cleaning pipe 8 is positioned by means of theunion nut 9. For cleaning, the tandem burner 21 is moved from theworking position into the starting position 22, and oriented in such amanner that the center line 23 of the tandem burner 21 lines up withthat of the cleaning pipe 8. From this position, the tandem burner 21 ispivoted by an angle 24, so that the contact pipe 25 lies on the centerline 14, together with the cleaning pipe 8. After orientation, thepivoted tandem burner 21 moves out of the starting position 22 into thefirst cleaning position 26. If the measurement device 4 confirms, bymeans of the signal 15, that CO₂ liquid is present, the robot gives thesignal 16 for opening the valve 3. The liquid CO₂ flows through thenozzle openings 17 into the cleaning pipe 8 and relaxes, withsimultaneous slight condensation, to form CO₂ snow that is blown ontothe exit opening of the gas nozzle 27 by means of the pressure in thebottle 1. The required pressure equalization is achieved by means of theequalization bores 20. Once part of the exit opening of the gas nozzle27 has been cleaned, the tandem burner 22 moves from the first cleaningposition 26 into the second cleaning position 28. In this connection,the contact pipe 25 moves into and the gas nozzle 27 moves over thecleaning pipe 8. Once the position 28 has been reached, the valve 3 isopened by means of the signal 16 and CO₂ snow is again blown into thecleaning pipe 8. Because of the contact pipe 25 being moved into thecleaning pipe 8, the CO₂ snow is necessarily guided past the contactpipe 25 and the inside surface of the gas nozzle 27. After successfulcleaning, the tandem burner 21 moves back into the starting position 22.The tandem burner 21 is pivoted, in this position, by the angle 24, intothe starting position, and further, by the same angle 24, towards theother side, in such a manner that the contact pipe 29 is on the samecenter line 14 with the cleaning pipe 8. Cleaning takes place in thesame manner as in the case of the contact pipe 25. After the secondcontact pipe has also been cleaned, the tandem burner moves back intothe starting position 22, pivots back into the starting position by theangle 24, and from there into the working position.

EXAMPLE 3

The cleaning pipe with inside bores 30 is set onto the cleaning head inExample 1 and positioned in place by means of the enlarged union nut 34.As a function of the cleaning program, the welding burner 10 moveseither into the first position 18 for cleaning the gas exit opening ofthe gas nozzle 13, whereby the liquid CO₂ is blown onto the gas exitopening directly ahead of the gas nozzle 13, out of the inside bores 31of the cleaning pipe with inside bores 30, forming CO₂ snow, orimmediately into the second cleaning position 19, where the compulsoryguidance of the CO₂ snow, which is influenced by the heat capacity thatis dependent on the material and thickness of the wall of the cleaningpipe with inside bore 30, cleans the contact pipe 12 and the inside wallof the gas nozzle 13 at the same time. To avoid build-up of pressure andin order to transport the welding spatters that are loosened by means ofthe thermotension, several ventilation bores 32 are made in the cleaningpipe with inside bores 30. To remove the loosened spatters along the gasnozzle from the cleaning pipe with inside bores 30, air exit openings 33are provided in the enlarged union nut 34.

EXAMPLE 4

The stepped cleaning pipe 35 is set onto the cleaning head 5 in Example1 and fixed in its position by means of the adapted union nut 36. As afunction of the cleaning program, the welding burner 10 moves eitherinto the position 18 for cleaning the gas exit opening of the gas nozzle13, or over the contact pipe 12 with the stepped region 37. The weldingburner 10 is moved so far over the contact pipe 12 until the nozzlecrown is situated in the position 19 and the nozzle crown 39 is situatedin the position 18. The nozzle crowns 38 and 39 become active by meansof activation of various valves. Cleaning takes place by means ofalternately or simultaneously turning on the valves. The stress-reliefbore 40 prevents build-up of pressure, and the air bores 41 eliminatethe residues from the stepped cleaning pipe 35.

REFERENCE SYMBOLS

-   1 CO₂ liquid tank-   2 pressure line-   3 valve-   4 measurement device-   5 cleaning head-   6 nut-   7 housing-   8 cleaning pipe-   9 union nut-   10 welding burner-   11 starting position-   12 contact pipe-   13 gas nozzle-   14 center line-   15 signal (CO₂ liquid)-   16 signal (valve)-   17 nozzle openings-   18 first cleaning position (single-wire burner)-   19 second cleaning position (single-wire burner)-   20 equalization bore-   21 tandem burner-   22 starting position-   23 center line-   24 angle-   25 contact pipe I-   26 first cleaning position (tandem burner)-   27 gas nozzle-   28 second cleaning position (tandem burner)-   29 contact pipe II-   30 cleaning pipe with interior bores-   31 interior bore-   32 ventilation bores-   33 air exit openings-   34 enlarged union nut-   35 stepped cleaning pipe-   36 adapted union nut-   37 stepped region-   38 nozzle crown-   39 nozzle crown-   40 stress-relief bore-   41 air bore

1: Method for cleaning welding burners, using a cold blasting agent,wherein the liquid CO₂, which is under pressure in a tank (1), isuniformly blown into an interchangeable cleaning sleeve (8) that isadapted to the burner, at the bottom of the cleaning sleeve (8), usingone or more jet nozzles (17), and that CO₂ snow is formed by thesimultaneous relaxation, which snow condenses because of the smallinside diameter of the cleaning sleeve (8) and the CO₂ that continues toflow in, and is partly converted to the gaseous state due to the heatcapacity of the cleaning sleeve (8), and, at the same time, is guidedonto a certain region of the burner (10) to be cleaned, compulsorilyguided by means of the pressure of the liquid CO₂ and the gas phase ofthe CO₂, which is increasing in volume, whereby the burner (10) supportsthis compulsory guidance by means of moving to several cleaningpositions (18, 19), and the loosened contaminants are removed from theburner region by means of the flows that occur, caused by the compulsoryguidance and supported by the equalization bores (20). 2: Methodaccording to claim 1, wherein blowing in of the liquid CO₂ into thecleaning pipe (8) takes place in interval-like manner. 3: Methodaccording to claim 1, wherein the sum of the exit surface of the jetnozzles (17), in order to obtain an effective condensation, must standin a certain ratio to the inside surface of the cleaning pipe (8). 4:Device for implementing the method for cleaning welding burners, using acold blasting agent, preferably CO₂ snow, wherein a cleaning pipe (8)that is adapted to the burner (10, 21) in terms of length, diameter, andshape, which pipe possesses one or more jet nozzles (17) for blowing inliquid CO₂ at its bottom, whereby the sum of the cross-sections of thejet nozzles (17) is adapted to the cleaning pipe (8) in terms of shapeand size, in a certain ratio, after orientation is situated on the samecenter line (14) with the contact pipes (12, 25, 29) in a position foraccommodation of the burner (10, 21), whereby the contact pipe (12, 25,29) moves into and the gas nozzle (13, 27) moves over the cleaning pipe(8), by means of displacement of the burner (10, 21). 5: Deviceaccording to claim 4, wherein the welding burner (10, 21) is fixed inplace and that movement to the cleaning positions (18, 19, 26, 28) andpassage over the cleaning pipe (8) by the welding burner (10, 21) isimplemented by means of the device, which is mounted on an axiallydisplaceable sled. 6: Device for implementing the method for cleaningwelding burners, using a cold blasting agent, preferably CO₂ snow,wherein a cleaning pipe with inside bores (30) that is adapted to theburner (10, 21) in terms of length, diameter, and shape can bepositioned relative to the welding burner (10, 21) in such a manner thatthe liquid CO₂ that flows out of the crown of the inside bores (31)under pressure, forming CO₂ snow, is directly guided onto the facesurface of the gas nozzle (13, 27) and subsequently the contact pipe(s)(12, 25, 29) move so far into the cleaning pipe with inside bores (30)that the welding burner (10) is cleaned from the inside, by means ofrenewed short-term inflow of liquid CO₂, with the simultaneous formationof CO₂ snow, whereby the CO₂ snow simultaneously cleans the contact pipe(12, 25, 29) and the inside surface of the gas nozzle (13, 27), wherebythe ventilation bores (32) prevent build-up of pressure, and allowoutflow of the CO₂ snow/gas mixture with the loosened contaminants. 7:Device for implementing the method for cleaning welding burners, using acold blasting agent, preferably CO₂ snow, wherein a stepped cleaningpipe (35) that is adapted to the burner (10, 21) in terms of length,diameter, and shape can be positioned relative to the welding burner(10), either in the first station, in such a manner that the liquid CO₂that flows out of the nozzle crown (38) under pressure, forming CO₂snow, directly impacts the exit opening of the gas nozzle (13, 27), orthat the stepped cleaning pipe (35), which corresponds to the differencebetween the positions (18, 19) with its stepped region (37), moves overthe contact pipe(s) (12, 25, 29) in such a manner that the nozzle crown(38) stands in the position (19) and the nozzle crown (39) stands in theposition (18), and the corresponding regions of the burner (10, 21) canbe cleaned simultaneously or at intervals, whereby the air exit openings(33) prevent build-up of pressure, and the air bores (41) allow cleaningof the stepped cleaning sleeve (35).